U.S. patent application number 11/429140 was filed with the patent office on 2006-10-19 for optical recording medium, method for manufacturing the same, sputtering target, method for using optical recording medium, and optical recording apparatus.
Invention is credited to Hiroshi Deguchi, Kazunori Ito, Masaki Kato, Hiroko Ohkura, Mikiko Takada.
Application Number | 20060233998 11/429140 |
Document ID | / |
Family ID | 34575939 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060233998 |
Kind Code |
A1 |
Takada; Mikiko ; et
al. |
October 19, 2006 |
Optical recording medium, method for manufacturing the same,
sputtering target, method for using optical recording medium, and
optical recording apparatus
Abstract
To provide an optical recording medium which can maintain
excellent recording characteristics and storage reliability even at
high recording speeds of 3.times. to 10.times. on DVD, particularly
at 8.times. or faster, and whose recording material can be readily
initialized to provide a uniform reflectivity distribution. The
optical recording medium includes a substrate, first protective
layer, recording layer, second protective layer and reflective
layer, the first protective layer, recording layer, second
protective layer and reflective layer being disposed on the
substrate in this order or in reverse order, wherein the recording
layer comprises a composition expressed by the Formula
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. where
X.sub.1 represents at least one element selected from Ga, Ge and
In; X.sub.2 represents at least one element selected from Au, Ag
and Cu; and .alpha., .beta. and .gamma. represent atomic % of their
respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10, and
(.alpha.+.beta.+.gamma.)=100).
Inventors: |
Takada; Mikiko;
(Yokohama-shi, JP) ; Ito; Kazunori; (Yokohama-shi,
JP) ; Deguchi; Hiroshi; (Yokohama-shi, JP) ;
Ohkura; Hiroko; (Yokohama-shi, JP) ; Kato;
Masaki; (Sagamihara-shi, JP) |
Correspondence
Address: |
COOPER & DUNHAM, LLP
1185 AVENUE OF THE AMERICAS
NEW YORK
NY
10036
US
|
Family ID: |
34575939 |
Appl. No.: |
11/429140 |
Filed: |
May 4, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP04/16635 |
Nov 10, 2004 |
|
|
|
11429140 |
May 4, 2006 |
|
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Current U.S.
Class: |
428/64.1 ;
G9B/7.142; G9B/7.198 |
Current CPC
Class: |
G11B 7/259 20130101;
Y10T 428/21 20150115; G11B 7/00454 20130101; G11B 2007/24308
20130101; G11B 2007/24312 20130101; G11B 2007/24314 20130101; G11B
7/2542 20130101; G11B 7/266 20130101; G11B 2007/2431 20130101; G11B
7/243 20130101; G11B 7/24067 20130101; G11B 7/2578 20130101; G11B
7/24038 20130101 |
Class at
Publication: |
428/064.1 |
International
Class: |
B32B 3/02 20060101
B32B003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2003 |
JP |
2003-379378 |
Mar 1, 2004 |
JP |
2004-056170 |
Claims
1. An optical recording medium comprising: a substrate; a first
protective layer; a recording layer; a second protective layer; and
a reflective layer, the first protective layer, recording layer,
second protective layer and reflective layer being disposed on the
substrate in this order or in reverse order, wherein the recording
layer comprises a composition expressed by the following Formula 1:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1> where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100).
2. The optical recording medium according to claim 1, wherein the
recording layer is expressed by the formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub.2).sub.-
.epsilon.Sn.sub..zeta.--Y.sub..eta. where X.sub.2 represents at
least one element selected from Au, Ag and Cu; Y represents at
least one element selected from Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg,
Se, C, N, Mn and Dy; and .alpha., .beta., .gamma., .delta.,
.epsilon., .zeta. and .eta. satisfy the following conditions:
0.ltoreq..alpha..ltoreq.20, 0.ltoreq..beta..ltoreq.20,
0.ltoreq..gamma..ltoreq.20 (provided .alpha., .beta. and .gamma.
are not "0" at the same time), 40.ltoreq..delta..ltoreq.95,
0<.epsilon..ltoreq.10, 0.ltoreq..zeta..ltoreq.40,
0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.zeta.+.eta.)=100).
3. The optical recording medium according to claim 1, wherein the
recording layer performs at least one of a recording operation, an
erasing operation and a rewriting operating by utilizing reversible
phase change between amorphous and crystalline phases.
4. The optical recording medium according to claim 1, wherein the
thickness of the recording layer is 6 nm to 20 nm.
5. The optical recording medium according to claim 1, wherein the
first protective layer and the second protective layer comprise a
mixture of ZnS and SiO.sub.2.
6. The optical recording medium according to claim 1, wherein the
reflective layer comprises one of Ag and an Ag alloy.
7. The optical recording medium according to claim 1, wherein a
sulfur-free third protective layer is provided between the second
protective layer and the reflective layer, and the sulfur-free
third protective layer comprises at least one of SiC and Si.
8. The optical recording medium according to claim 1, wherein an
oxide-containing interface layer is provided at least between the
recording layer and the first protective layer or between the
recording layer and the second protective layer.
9. The optical recording medium according to claim 1, wherein the
reflectivity uniformity, expressed by the following Expression 1,
of an initialized non-recorded portion to a recording and
reproduction laser beam is 0.10 or less. Reflectivity
uniformity=(maximum reflectivity value-minimum reflectivity
value)/average of reflectivity values. <Expression 1>
10. The optical recording medium according to claim 1, wherein the
substrate comprises a wobble groove of 0.74.+-.0.03 .mu.m in pitch,
22 nm to 40 nm in depth, and 0.2 .mu.m to 0.4 .mu.m in width.
11. The optical recording medium according to claim 1, capable of
recording at 3.times. to 10.times.DVD recording speeds.
12. An optical recording medium comprising: a substrate; a first
protective layer; a recording layer; a second protective layer; and
a reflective layer, the first protective layer, recording layer,
second protective layer and reflective layer being disposed on the
substrate in this order or in reverse order, wherein the recording
layer comprises a composition expressed by the following Formula 2:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
<Formula 2> where X.sub.1 represents at least one element
selected from Ga, Ge and In; X.sub.2 represents at least one
element selected from Au, Ag and Cu; M represents at least one
element selected from elements other than X.sub.1, Sb and X.sub.2
and mixtures of the elements other than X.sub.1, Sb and X.sub.2;
and .alpha., .beta., .gamma. and .delta. represent atomic % of
their respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10,
0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
13. The optical recording medium according to claim 12, wherein M
represents at least one element selected from Te, Al, Zn, Mg, Tl,
Pb, Sn, Bi, Cd, Hg, Se, C, N, Mn and Dy.
14. The optical recording medium according to claim 12, wherein the
recording layer comprises a composition expressed by the following
Formula 3:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.--Sn.sub..delta.
<Formula 3> where X.sub.1 represents at least one element
selected from Ga, Ge and In; X.sub.2 represents at least one
element selected from Au, Ag and Cu; and .alpha., .beta., .gamma.
and .delta. represent atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
15. The optical recording medium according to claim 12, wherein the
recording layer is expressed by the formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub.2).sub.-
.epsilon.Sn.sub..zeta.--Y.sub..eta. where X.sub.2 represents at
least one element selected from Au, Ag and Cu; Y represents at
least one element selected from Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg,
Se, C, N, Mn and Dy; and .alpha., .beta., .gamma., .delta.,
.epsilon., .zeta. and .eta. satisfy the following conditions:
0.ltoreq..alpha..ltoreq.20, 0.ltoreq..beta..ltoreq.20,
0.ltoreq..gamma..ltoreq.20 (provided .alpha., .beta. and .gamma.
are not "0" at the same time), 40.ltoreq..delta..ltoreq.95,
0<.epsilon..ltoreq.10, 0.ltoreq..zeta..ltoreq.40,
0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.GAMMA.+.epsilon.+.zeta.+.eta.)=100).
16. The optical recording medium according to claim 12, wherein the
recording layer performs at least one of a recording operation, an
erasing operation and a rewriting operating by utilizing reversible
phase change between amorphous and crystalline phases.
17. The optical recording medium according to claim 12, wherein the
thickness of the recording layer is 6 nm to 20 nm.
18. The optical recording medium according to claim 12, wherein the
first protective layer and the second protective layer comprise a
mixture of ZnS and SiO.sub.2.
19. The optical recording medium according to claim 12, wherein the
reflective layer comprises one of Ag and an Ag alloy.
20. The optical recording medium according to claim 12, wherein a
sulfur-free third protective layer is provided between the second
protective layer and the reflective layer, and the sulfur-free
third protective layer comprises at least one of SiC and Si.
21. The optical recording medium according to claim 12, wherein an
oxide-containing interface layer is provided at least between the
recording layer and the first protective layer or between the
recording layer and the second protective layer.
22. The optical recording medium according to claim 12, wherein the
reflectivity uniformity, expressed by the following Expression 1,
of an initialized non-recorded portion to a recording and
reproduction laser beam is 0.10 or less. Reflectivity
uniformity=(maximum reflectivity value-minimum reflectivity
value)/average of reflectivity values. <Expression 1>
23. The optical recording medium according to claim 12, wherein the
substrate comprises a wobble groove of 0.74.+-.0.03 .mu.m in pitch,
22 nm to 40 nm in depth, and 0.2 .mu.m to 0.4 .mu.m in width.
24. The optical recording medium according to claim 12, capable of
recording at 3.times. to 10.times.DVD recording speeds.
25. A sputtering target used for the production of a recording
layer, the sputtering target comprising: a composition expressed by
the following Formula 1:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1> where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100).
26. The sputtering target according to claim 25, expressed by the
formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub.2).sub.-
.epsilon.Sn.sub..zeta.--Y.sub..eta. where X.sub.2 represents at
least one element selected from Au, Ag and Cu; Y represents at
least one element selected from Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg,
Se, C, N, Mn and Dy; and .alpha., .beta., .gamma., .delta.,
.epsilon., .zeta. and .eta. satisfy the following conditions:
0.ltoreq..alpha..ltoreq.20, 0.ltoreq..beta..ltoreq.20,
0.ltoreq..gamma..ltoreq.20 (provided .alpha., .beta. and .gamma.
are not "0" at the same time), 40.ltoreq..delta..ltoreq.95,
0<.epsilon..ltoreq.10, 0.ltoreq..zeta..ltoreq.40,
0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.zeta.+.eta.)=100).
27. A sputtering target used for the production of a recording
layer, the sputtering target comprising: a composition expressed by
the following Formula 2:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
[Formula 2] where X.sub.1 represents at least one element selected
from Ga, Ge and In; X.sub.2 represents at least one element
selected from Au, Ag and Cu; M represents at least one element
selected from elements other than X.sub.1, Sb and X.sub.2 and
mixtures of the elements other than X.sub.1, Sb and X.sub.2; and
.alpha., .beta., .gamma. and .delta. represent atomic % of their
respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10,
0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
28. The sputtering target according to claim 27, wherein M
represents at least one element selected from Te, Al, Zn, Mg, Tl,
Pb, Sn, Bi, Cd, Hg, Se, C, N, Mn and Dy.
29. The sputtering target according to claim 27, comprising a
composition expressed by the following Formula 3:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.--Sn.sub..delta.
[Formula 3] where X.sub.1 represents at least one element selected
from Ga, Ge and In; X.sub.2 represents at least one element
selected from Au, Ag and Cu; and .alpha., .beta., .gamma. and
.delta. represent atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
30. The sputtering target according to claim 27, expressed by the
formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub.2).sub.-
.epsilon.Sn.sub..zeta.--Y.sub..eta. where X.sub.2 represents at
least one element selected from Au, Ag and Cu; Y represents at
least one element selected from Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg,
Se, C, N, Mn and Dy; and .alpha., .beta., .gamma., .delta.,
.epsilon., .zeta. and .eta. satisfy the following conditions:
0.ltoreq..alpha..ltoreq.20, 0.ltoreq..beta..ltoreq.20,
0.ltoreq..gamma..ltoreq.20 (provided .alpha., .beta. and .gamma.
are not "0" at the same time), 40.ltoreq..delta..ltoreq.95,
0<.epsilon..ltoreq.10, 0.ltoreq..zeta..ltoreq.40,
0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.zeta.+.eta.)=100).
31. A method for manufacturing an optical recording medium,
comprising: forming a recording layer with a sputtering method
using a sputtering target, wherein the sputtering target comprises
a composition expressed by the following Formula 1:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1> where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100), and
wherein the optical recording medium comprises: a substrate; a
first protective layer; the recording layer; a second protective
layer; and a reflective layer, the first protective layer,
recording layer, second protective layer and reflective layer being
disposed on the substrate in this order or in reverse order.
32. A method for manufacturing an optical recording medium,
comprising: forming a recording layer with a sputtering method
using a sputtering target, wherein the sputtering target comprises
a composition expressed by the following Formula 2:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
[Formula 2] where X.sub.1 represents at least one element selected
from Ga, Ge and In; X.sub.2 represents at least one element
selected from Au, Ag and Cu; M represents at least one element
selected from elements other than X.sub.1, Sb and X.sub.2 and
mixtures of the elements other than X.sub.1, Sb and X.sub.2; and
.alpha., .beta., .gamma. and .delta. represent atomic % of their
respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10,
0<.delta..ltoreq.40, and (.alpha.+.beta.+.gamma.+.delta.)=100),
and wherein the optical recording medium comprises: a substrate; a
first protective layer; the recording layer; a second protective
layer; and a reflective layer, the first protective layer,
recording layer, second protective layer and reflective layer being
disposed on the substrate in this order or in reverse order.
33. A method for using an optical recording medium, comprising:
applying a laser beam onto an optical recording medium from the
first protective layer side to perform at least one of a recording
operation, an erasing operation and a rewriting operation, wherein
the optical recording medium comprises: a substrate; a first
protective layer; a recording layer; a second protective layer; and
a reflective layer, the first protective layer, recording layer,
second protective layer and reflective layer being disposed on the
substrate in this order or in reverse order, wherein the recording
layer comprises a composition expressed by the following Formula 1:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1> where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100).
34. A method for using an optical recording medium, comprising:
applying a laser beam onto an optical recording medium from the
first protective layer side to perform at least one of a recording
operation, an erasing operation and a rewriting operation, wherein
the optical recording medium comprises: a substrate; a first
protective layer; a recording layer; a second protective layer; and
a reflective layer, the first protective layer, recording layer,
second protective layer and reflective layer being disposed on the
substrate in this order or in reverse order, wherein the recording
layer comprises a composition expressed by the following Formula 2:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
<Formula 2> where X.sub.1 represents at least one element
selected from Ga, Ge and In; X.sub.2 represents at least one
element selected from Au, Ag and Cu; M represents at least one
element selected from elements other than X.sub.1, Sb and X.sub.2
and mixtures of the elements other than X.sub.1, Sb and X.sub.2;
and .alpha., .beta., .gamma. and .delta. represent atomic % of
their respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10,
0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
35. An optical recording apparatus for applying a laser beam onto
an optical recording medium from a laser beam source to thereby
perform at least one of a recording operation, an erasing operation
and a rewriting operation on the optical recording medium, wherein
the optical recording medium comprises: a substrate; a first
protective layer; a recording layer; a second protective layer; and
a reflective layer, the first protective layer, recording layer,
second protective layer and reflective layer being disposed on the
substrate in this order or in reverse order, wherein the recording
layer comprises a composition expressed by the following Formula 1:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1> where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from A, Ag and Cu; and .alpha., .beta. and .gamma. represent atomic
% of their respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10, and
(.alpha.+.beta.+.gamma.)=100).
36. An optical recording apparatus for applying a laser beam onto
an optical recording medium from a laser beam source to thereby
perform at least one of a recording operation, an erasing operation
and a rewriting operation on the optical recording medium, wherein
the optical recording medium comprises: a substrate; a first
protective layer; a recording layer; a second protective layer; and
a reflective layer, the first protective layer, recording layer,
second protective layer and reflective layer being disposed on the
substrate in this order or in reverse order, wherein the recording
layer comprises a composition expressed by the following Formula 2:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
<Formula 2> where X.sub.1 represents at least one element
selected from Ga, Ge and In; X.sub.2 represents at least one
element selected from Au, Ag and Cu; M represents at least one
element selected from elements other than X.sub.1, Sb and X.sub.2
and mixtures of the elements other than X.sub.1, Sb and X.sub.2;
and .alpha., .beta., .gamma. and .delta. represent atomic % of
their respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10,
0<.delta..ltoreq.40, and (.alpha.+.beta.+.gamma.+.delta.)=100).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of Application PCT/JP2004/016635,
filed on Nov. 10, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical recording medium
(hereinafter sometimes referred to as a "phase-change optical
information recording medium", "phase-change optical recording
medium", or "optical information recording medium") which can
maintain excellent recording characteristics and storage
reliability even at high recording speeds of 3.times. to 10.times.
on DVD, particularly at 8.times. or faster, and whose recording
material can be readily initialized to provide a uniform
reflectivity distribution; a method for manufacturing the same; a
sputtering target; a method for using the optical recording medium;
and an optical recording apparatus.
[0004] 2. Description of the Related Art
[0005] So-called phase-change optical recording media that utilize
a transition between crystalline and amorphous phases have been
known as one of rewritable optical recording media where
information is erasable by irradiation with a semiconductor laser
beam. The phase-change optical recording media realize repetitive
recording with a single beam irradiation and require a simple
optical system on the drive side. For these reasons, they are now
widely used as optical recording media in many fields including
computers, pictures, and audio. Optical recording media (e.g.,
CD-R, CD-RW and DVD) recording speed has been increased along with
extensive worldwide distribution. It is now demanded that optical
recording media have increased storage capacity and density enough
to support, for example, high-density image recording. Against this
backdrop, attempts have been made to achieve recording at higher
speeds.
[0006] The optical information recording medium is generally
constituted of a substrate and a recording layer provided on the
substrate, and generally, a translucent protective layer with heat
resistance is provided on both sides of the recording layer. In
addition, a reflective layer is provided on the opposite side of
the protective layer from the side where a light beam is incident.
In the optical information recording medium, information can be
recorded or erased only by changing laser beam power; crystallized
portions of the recording layer serve both as non-recorded areas
and information-erased area, and amorphous portions serve as
recording marks (amorphous marks).
[0007] In the optical recording medium a focused, pulsed laser beam
of three different output levels is used to switch the recording
layer back and force between crystalline and amorphous phases. At
this point, the pulse of maximum output level serves to melt the
recording layer, the pulse of intermediate output level serves to
heat the recording layer to temperatures higher than its
crystallization temperature but just below its melting point, and
the pulse of minimum output level serves to control the heating or
cooling of the recording layer. The recording layer that has melted
as a result of irradiation with a laser pulse of maximum output
level then undergoes rapid cooling down, changing to an amorphous
or microcrystal state to cause a reduction in the reflectivity. In
this way the amorphous or microcrystal portion of the recording
layer function as a recording mark. Meanwhile, a portion of the
recording layer irradiated with a laser pulse of intermediate
output level completely becomes crystalline, whereby information
can be erased. In this way alternating crystalline areas and
amorphous areas can be formed on the recording layer by changing
the writing laser pulse output levels, recording information on the
recording layer.
[0008] In order to achieve high-speed recording in the optical
recording medium, its recording layer requires phase-change
materials that rapidly crystallizes. For such phase-change
materials, Sb--Te phase-change materials doped with Ga, Ge, In and
the like have been used (see Japanese Patent Application Laid-Open
(JP-A) No. 60-179954, 05-286249, 07-065414, 07-120867, 08-212604,
2000-190637, 2000-339750, 2001-067722, 2002-264514, 2002-283726,
2002-331758 and 2003-006859; Japanese Patent Application
Publication (JP-B) No. 03-052651, 04-001933; Japanese Patent (JP-B)
No. 2941848 and 3214210; and "Phase-Change optical data storage in
GaSb", Applied Opticas, Vol. 26, No. 22115, November, 1987). This
is because chalcogen elements (S, Se and Te) feature the ability to
bind to many elements to create many different amorphous phases.
For this reason, chalcogen elements, especially Te, have been
received attention as essential constituents of phase-change
materials.
[0009] For high-speed recording, acceleration of the
crystallization rate of a recording layer is not enough; it is also
necessary to ensure the stability of amorphous portions (marks).
Although the use of recording materials with high crystallization
rate leads to poor stability in amorphous portions, the use of
recording materials with high crystallization rate but with high
crystallization temperature can ensure the stability of formed
marks for a long period of time. For example, there is a report
that Ga--Sb phase-change materials, known as recording materials
for high-speed recording, have significantly high crystallization
rate and crystallization temperature, which is as high as
350.degree. C. (see "Phase-Change optical data storage in GaSb",
Applied Opticas, Vol. 26, No. 22115, November, 1987). The use of
such recording materials realizes the provision of an optical
recording medium which is capable of recording at 8.times.DVD
recording speed or faster, as well as excellent in mark stability.
These recording materials, however, have a severe drawback: "poor
initialization performance". Such recording materials cannot be
readily initialized because of their high crystallization
temperature. Even when they are initialized by applying a
high-energy beam, there are fluctuations in the reflectivity from
one portion to another on the initialized region of the disc,
adversely affecting its recording characteristics.
[0010] Accordingly, there has yet been no optical recording medium
which can maintain excellent recording characteristics and storage
reliability even at high recording speeds of 3.times. to 10.times.
on DVD, particularly at 8.times. or faster, and whose recording
material can be readily initialized to provide a uniform
reflectivity distribution. It is demanded that such an optical
recording medium be provided as soon as possible.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to solve the
conventional problems and, in response to the demand as described
above, to provide an optical recording medium which can maintain
excellent recording characteristics and storage reliability even at
high recording speeds of 3.times. to 10.times. on DVD, particularly
at 8.times. or faster, and whose recording material can be readily
initialized to provide a uniform reflectivity distribution; a
method for manufacturing the same; a sputtering target; a method
for using an optical recording medium; and an optical recording
apparatus.
[0012] The present inventors have focused attention on Ga--Sb
materials that are potentially suitable for high-speed recording
during the development of optical recording media that can support
high-speed recording as fast as 3.times. to 10.times.DVD recording
speeds, particularly as fast as 8.times. or faster, and have
diligently conducted studies. As a result, they have established
that it is possible to solve the problems associated with
initialization of the recording layer by uniformly dispersing
crystalline particles made of at least one element selected from
Au, Ag and Cu in the Ga--Sb material of the recording layer. They
have also established that by adding Sn and the like in the Ga--Sb
material it is possible to provide an optical recording medium
which can ensure excellent recording characteristics and storage
reliability even at high recording speeds of 8.times. or faster on
DVD.
[0013] The present invention has been accomplished based on the
findings by the present inventors. The followings are means for
solving the foregoing problems.
[0014] <1> An optical recording medium having a substrate, a
first protective layer, a recording layer, a second protective
layer, a reflective layer, the first protective layer, recording
layer, second protective layer and reflective layer being disposed
on the substrate in this order or in reverse order, wherein the
recording layer comprises a composition expressed by the following
Formula 1: (X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.
<Formula 1>
[0015] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100).
[0016] The optical recording medium according to the first
embodiment of the present invention comprises the foregoing
composition. Thus, it is possible to provide an optical recording
medium which can realize excellent recording characteristics and
storage reliability even at high recording speed of 8.times. on DVD
(about 28 m/s) and whose recording material can be readily
initialized to provide a uniform reflectivity distribution.
[0017] <2> An optical recording medium having a substrate, a
first protective layer, a recording layer, a second protective
layer, and a reflective layer, the first protective layer,
recording layer, second protective layer and reflective layer being
disposed on the substrate in this order or in reverse order,
wherein the recording layer comprises a composition expressed by
the following Formula 2:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
<Formula 2>
[0018] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; M represents at least one element selected from
elements other than X.sub.1, Sb and X.sub.2 and mixtures of the
elements other than X.sub.1, Sb and X.sub.2; and .alpha., .beta.,
.gamma. and .delta. represent atomic % of their respective elements
(where 2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
[0019] The optical recording medium according to the second
embodiment of the present invention comprises the foregoing
composition. Thus, it is possible to provide an optical recording
medium which can realize excellent recording characteristics and
storage reliability even at high recording speeds of 3.times. to
10.times. on DVD, particularly at 8.times. or faster, and whose
recording material can be readily initialized to provide a uniform
reflectivity distribution.
[0020] <3> The optical recording medium according to
<2>, wherein M represents at least one element selected from
Te, Al, Zn, Mg, Tl, Pb, Sn, Bi, Cd, Hg, Se, C, N, Mn and Dy. In the
optical recording medium according to <3>, any of Te, Al, Zn,
Mg, Tl, Pb, Sn, Bi, Cd, Hg, Se, C, N, Mn and Dy has an effect of
increasing the crystallization rate, whereby high-speed recording
is made possible. These elements, however, are less potent in
increasing the crystallization rate while keeping excellent
recording characteristics than Ga and In. The total amount of these
elements is preferably 20 atomic % or less. In addition, Te, Al,
Zn, Se, C and N also have an effect of improving storage
reliability, though they are less potent than Ge.
[0021] <4> The optical recording medium according to one of
<2> and <3>, wherein the recording layer comprises a
composition expressed by the following Formula 3. The optical
recording medium according to <4> comprises Sn as an
essential constituent. Sn not only has an effect of increasing the
crystallization rate as do Ga and In, but also is advantageous over
Ga and In in terms of the capability of lowering the melting point
of recording material, improving the sensitivity of recording
media, increasing reflectivity, and reducing initialization noises.
Thus, Sn is an excellent additive element that can increase
recording characteristics in a comprehensive manner. If the content
of Sn is greater than 40 atomic %, it results in too high
crystallization rate, making it difficult for the recording layer
to be amorphized.
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.--Sn.sub..delta.
<Formula 3>
[0022] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta., .gamma. and .delta.
represent atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
[0023] <5> The optical recording medium according to any one
of <1> to <5>, wherein the recording layer is expressed
by the formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub-
.2).sub..epsilon.Sn.sub..zeta.--Y.sub..eta. where X.sub.2
represents at least one element selected from Au, Ag and Cu; Y
represents at least one element selected from Te, Al, Zn, Mg, Tl,
Pb, Bi, Cd, Hg, Se, C, N, Mn and Dy; and .alpha., .beta., .gamma.,
.delta., .epsilon., .zeta. and .eta. satisfy the following
conditions: 0.ltoreq..alpha..ltoreq.20, 0.ltoreq..beta..ltoreq.20,
0.ltoreq..gamma..ltoreq.20 (provided .alpha., .beta. and .gamma.
are not "0" at the same time), 40.ltoreq..delta..ltoreq.95,
0<.epsilon..ltoreq.10, 0.ltoreq..zeta..ltoreq.40,
0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.zeta.+.eta.)=100).
[0024] <6> The optical recording medium according to any one
of <1> to <5>, wherein the recording layer performs at
least one of a recording operation, an erasing operation and a
rewriting operating by utilizing reversible phase change between
amorphous and crystalline phases.
[0025] <7> The optical recording medium according to any one
of <1> to <6>, wherein the thickness of the recording
layer is 6 nm to 20 nm.
[0026] <8> The optical recording medium according to any one
of <1> to <7>, wherein the first protective layer and
the second protective layer comprise a mixture of ZnS and
SiO.sub.2. The first protective layer and the second protective
layer in the optical recording medium according to <8>
comprise a mixture of ZnS and SiO.sub.2. The mixture of ZnS and
SiO.sub.2 imparts high heat resistance, low thermal conductivity,
and excellent chemical stability to these protective layers. In
such protective layers containing the mixture of ZnS and SiO.sub.2,
film residual stress is small and there is a low likelihood that
recording characteristics (e.g., recording sensitivity and
information-erasing rate) would be reduced after recording-erasing
cycles. In addition, such protective layers are also advantageous
in that they have excellent adhesion with the recording layer.
[0027] <9> The optical recording medium according to any one
of <1> to <8>, wherein the reflective layer comprises
one of Ag and an Ag alloy. In the optical recording medium
according to <9>, Ag and an AG alloy have extremely high
thermal conductivity and thus can realize a rapid cooling mechanism
suitable for the formation of amorphous, by which the recording
layer that has reached a high temperature is immediately cooled
down. Thus, it is possible to form an excellent reflective
layer.
[0028] <10> The optical recording medium according to any one
of <1> to <9>, wherein a sulfur-free third protective
layer is provided between the second protective layer and the
reflective layer, and the sulfur-free third protective layer
comprises at least one of SiC and Si. If a reflective layer
contains Ag as does the recording of the optical recording medium
according to <1>, the use of a sulfur-containing material
(e.g., a mixture of ZnS and SiO.sub.2) for the second protective
layer causes sulfur to react with Ag, corroding the reflective
layer. Sulfuration of Ag can be prevented by providing such a third
protective layer between the second protective layer and the
reflective layer. In this way it is possible to ensure the
reliability of the optical recording medium.
[0029] <11> The optical recording medium according to any one
of <1> to <10>, wherein an oxide-containing interface
layer is provided at least between the recording layer and the
first protective layer or between the recording layer and the
second protective layer.
[0030] <12> The optical recording medium according to any one
of <1> to <11>, wherein the reflectivity uniformity,
expressed by the following Expression 1, of an initialized
non-recorded portion to a recording and reproduction laser beam is
0.10 or less. Reflectivity uniformity=(maximum reflectivity
value-minimum reflectivity value)/average of reflectivity values.
<Expression 1>
[0031] In the optical recording medium according to <12> the
fluctuations in the reflectivity of initialized (or crystallized)
portions significantly affect the recording characteristics, making
it difficult to provide uniform recording characteristics over all
date areas in the disc. It is possible to ensure uniform recording
characteristics by setting the reflectivity uniformity--expressed
by the foregoing Expression 1--to 0.10 or less.
[0032] <13> The optical recording medium according to any one
of <1> to <12>, wherein the substrate comprises a
wobble groove of 0.74.+-.0.03 .mu.m in pitch, 22 nm to 40 nm in
depth, and 0.2 .mu.m to 0.4 .mu.m in width. With this optical
recording medium according to <13> it is possible to provide
a DVD+RW medium, which is compliant with the current DVD+RW
standard and capable of high-speed recording. A wobble groove
realizes accessing a particular non-recorded track, as well as
rotation of the substrate at a constant linear velocity.
[0033] <14> The optical recording medium according to any one
of <1> to <13>, capable of recording at 3.times. to
10.times.DVD recording speeds. The optical recording medium
according to <14> is compliant with the current DVD+RW
standard and can record at 3.times. to 10.times. recording
speeds--about 10 m/s to 36 m/s.
[0034] <15> A sputtering target used for the production of a
recording layer, the sputtering target having a composition
expressed by the following Formula 1:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1>
[0035] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95 ,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100).
[0036] <16> A sputtering target used for the production of a
recording layer, the sputtering target having a composition
expressed by the following Formula 2:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
[Formula 2]
[0037] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; M represents at least one element selected from
elements other than X.sub.1, Sb and X.sub.2 and mixtures of the
elements other than X.sub.1, Sb and X.sub.2; and .alpha., .beta.,
.gamma. and .delta. represent atomic % of their respective elements
(where 2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
[0038] <17> The sputtering target according to <16>,
wherein M represents at least one element selected from Te, Al, Zn,
Mg, Tl, Pb, Sn, Bi, Cd, Hg, Se, C, N, Mn and Dy.
[0039] <18> The sputtering target according to one of
<16> and <17>, having a composition expressed by the
following Formula 3:
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.--Sn.sub..delt-
a. [Formula 3]
[0040] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta., .gamma. and .delta.
represent atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100).
[0041] <19> The sputtering target according to any one of
<15> to <18>, expressed by the formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub.2).sub.-
.epsilon.Sn.sub..zeta.--Y.sub..eta.
[0042] where X.sub.2 represents at least one element selected from
Au, Ag and Cu; Y represents at least one element selected from Te,
Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg, Se, C, N, Mn and Dy; and .alpha.,
.beta., .gamma., .delta., .epsilon., .zeta. and .eta. satisfy the
following conditions: 0.ltoreq..alpha..ltoreq.20,
0.ltoreq..beta..ltoreq.20, 0.ltoreq..gamma..ltoreq.20 (provided
.alpha., .beta. and .gamma. are not "0" at the same time),
40.ltoreq..delta..ltoreq.95, 0.ltoreq..epsilon..ltoreq.10,
0.ltoreq..zeta..ltoreq.40, 0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.zeta.+.eta.)=100).
[0043] In the sputtering target according to any one of <15>
to <18> it is possible to provide a desired recording layer
composition by forming the recording layer with a sputtering method
using an alloy target of desired composition. It is also possible
to inexpensively provide an optical recording medium which can
realize excellent recording characteristics and storage reliability
even at high recording speeds of 3.times. to 10.times. on DVD,
particularly at 8.times. or faster, and whose recording material
can be readily initialized to provide a uniform reflectivity
distribution.
[0044] <20> A method for manufacturing an optical recording
medium, including: forming a recording layer with a sputtering
method using a sputtering target according to any one of <15>
to <19>.
[0045] In the method of the present invention for manufacturing an
optical recording medium, a recording layer is formed with a
sputtering method using the sputtering target of the present
invention. Thus, it is possible to efficiently manufacture an
optical recording medium which can realize excellent recording
characteristics and storage reliability even at high recording
speeds of 3.times. to 10.times. on DVD, particularly at 8.times. or
faster, and whose recording material can be readily initialized to
provide a uniform reflectivity distribution
[0046] <21> A method for using an optical recording medium,
including: applying a laser beam onto an optical recording medium
according to any one of <1> to <14> from the first
protective layer side to perform at least one of a recording
operation, an erasing operation and a rewriting operation.
[0047] In the method of the present invention for using an optical
recording medium, a laser beam is applied onto the optical
recording medium of the present invention from the first protective
layer side to perform at least one of a recording operation, an
erasing operation and a rewriting operation. Thus, it is possible
to perform at least one of a recording operation, an erasing
operation and a rewriting operation stably and reliably.
[0048] <22> An optical recording apparatus for applying a
laser beam onto an optical recording medium from a laser beam
source to thereby perform at least one of a recording operation, an
erasing operation and a rewriting operation on the optical
recording medium, wherein the optical recording medium is an
optical recording medium according to any one of <1> to
<14>.
[0049] In the optical recording apparatus of the present invention
for applying a laser beam onto an optical recording medium from a
laser beam source to thereby perform at least one of a recording
operation, an erasing operation and a rewriting operation on the
optical recording medium, the optical recording medium of the
present invention is used. With this optical recording apparatus,
it is possible to perform at least one of a recording operation, an
erasing operation and a rewriting operation stably and
reliably.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a schematic cross-sectional view of an example of
an optical recording medium of the present invention.
[0051] FIG. 2 is a schematic cross-sectional view of another
example of the optical recording medium of the present
invention.
[0052] FIG. 3 is a schematic cross-sectional view of still another
example of the optical recording medium of the present
invention.
[0053] FIG. 4 is a schematic cross-sectional view of yet another
example of the optical recording medium of the present
invention.
[0054] FIG. 5 is an explanatory drawing of an example of the layer
structure of a double-layer optical recording medium of the present
invention.
[0055] FIG. 6 is an explanatory drawing of an example of the layer
structure of the optical recording medium of the present
invention.
[0056] FIG. 7 shows the state of an initialized recording layer in
Comparative Example 1, observed with a transmission electron
microscope.
[0057] FIG. 8 is a plot of optical disc reflectivities against
irradiation beam linear velocities.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(Optical Recording Medium)
[0058] The optical recording medium of the present invention
comprises a substrate, a first protective layer on the substrate, a
recording layer on the first protective layer, a second protective
layer on the recording layer, and a reflective layer on the second
protective layer. Alternatively, the optical recording medium of
the present invention comprises a substrate, a reflective layer on
the substrate, a second protective layer on the reflective layer, a
recording layer on the second protective layer, and a first
protective layer on the recording layer. The optical recording
medium of the present invention comprises an additional layer on an
as-needed basis.
[0059] The optical recording medium of the present invention is
irradiated with a laser beam from the first protective layer side,
whereby at least one of a recording operation, reproduction
operation, erasing operation, and rewriting operation is
performed.
--Recording Layer--
[0060] The recording layer is irradiated with a laser beam to
switch between crystalline and amorphous phases, thereby recording
and erasing signals. In this case, the crystalline phase and
amorphous phase are different from each other in terms of
reflectivity. In general, the crystalline phase with high
reflectivity serves as a non-recorded area. A high-energy laser
pulse is then applied to the crystalline phase to heat the
recording layer, followed by rapid cooling down. In this way
amorphous marks of low reflectivity are recorded as signals.
[0061] In the first embodiment, the recording layer of the optical
recording medium of the present invention contains a composition
expressed by the following Formula 1 as a phase-change material
that can maintain excellent recording characteristics and storage
reliability even at high recording speeds of 3.times. to 10.times.
on DVD, particularly at 8.times. or faster, and whose recording
material can be readily initialized to provide a uniform
reflectivity distribution.
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1>
[0062] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100)
[0063] In this case, the recording layer preferably contains a
composition expressed by the Following formula (1-1).
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1-1>
[0064] where X.sub.1 and X.sub.2 are identical to those in Formula
1; and .alpha., .beta., and .gamma. represent atomic % of their
respective elements (where 4.ltoreq..alpha..ltoreq.8,
84.ltoreq..beta..ltoreq.92, 4.ltoreq..gamma..ltoreq.8, and
(.alpha.+.beta.+.gamma.)=100)
[0065] Phase-change materials that contain Sb, a main constituent
of the recording layer, are excellent phase-change materials that
can realize high-speed recording, and its crystallization rate can
be adjusted by changing the Sb ratio; the higher the Sb ratio, the
higher the crystallization rate. If Sb is used singly, however, it
is difficult to provide recording layer materials with excellent
storage reliability as well as with high crystallization rate that
can support high-speed recording as fast as 8.times.DVD recording
speed (about 28 m/s). For this reason, at least one element
selected from Ga and In is added to the recording layer material to
increase the crystallization rate without reducing overwrite
characteristics and storage reliability. In addition, at least one
element selected from Ge and In is added to the recording layer
material to improve storage reliability. More preferably, Ge is
added.
[0066] The element Ga can increase both the crystallization rate
and crystallization temperature of phase-change material even when
added in small amounts. Thus, the addition of Ga is highly
effective to increase the stability (or storage reliability) of
marks.
[0067] The element Ge--when added in small amounts--does not
increase the crystallization rate but can significantly increase
the storage reliability of marks without increasing the
crystallization temperature to a level equal to or higher than that
achieved by Ga. For this reason, Ge is also an important element,
as is Ga.
[0068] The element In has a similar effect as Ga and increases the
crystallization temperature to a level lower than that achieved by
Ga. For this reason, in view of problems associated with
initialization, it is effective to use In as a supportive element
for Ga.
[0069] Accordingly, it is possible to design recording materials
with have high crystallization rate and excellent storage
reliability that can support high-speed recording, by changing the
elemental ratios of X.sub.1--Sb phase-change materials (where
X.sub.1 represents at least one element selected from Ga, Ge and
In). As described above, these materials, however, have a drawback
that they have high crystallization temperature, which leads to
poor initialization performance.
[0070] By changing the elemental ratios of Ga--Sb phase-change
materials, Ge--Sb phase-change materials, and In--Sb phase-change
materials, it is possible to design recording materials with high
crystallization rate and excellent storage reliability that can
support high-speed recording--specifically, recording speeds of
3.times. to 10.times. on DVD, particularly 8.times. or faster. As
described above, these materials, however, have a drawback that
they have high crystallization temperature, which leads to poor
initialization. To avoid this problem, at least one element
selected from Au, Ag and Cu is added to these phase-change
materials. One of the reasons why poor initialization performance
improves by the addition of at least one of these elements is that
these elements exist as crystalline particles in the recording
material and serve as "crystal nuclei" upon initialization to
facilitate crystallization (see FIG. 7, which shows the state of an
initialized recording layer observed with a transmission electron
microscope).
[0071] Accordingly, it is possible to solve the problems associated
with initialization of materials with high crystallization rates by
adding at least one element selected from Au, Ag and Cu in the
recording layer to form crystalline particles to thereby create
"crystal nuclei" in the recording layer beforehand.
[0072] Crystalline metal particles are produced by the following
Reaction 1: nX.sub.2.sup.0+heat.fwdarw.(X.sub.2.sup.0)n
(crystalline particles) [Reaction 1] where X.sub.2.sup.0 is a metal
atom present in a recording layer
[0073] In addition, when a metal atom in a recording layer is
present in the form of ions, crystalline particles may be produced
by the following Reaction 2:
X.sub.2+Sb.sup.2++h.nu..fwdarw.X.sub.2.sup.0+Sb.sup.4+ (reduction
reaction by Sb) [Reaction 2]
[0074] This reduction reaction by Sb is generally a photosensitive
reaction, and the reaction proceeds by the irradiation with
ultraviolet rays or the like. In this case, for example, metal
atoms are produced as a result of application of ultraviolet rays
used for curing of ultraviolet-curable resin.
[0075] In each case, heat generated as a result of the application
of laser during an initialization operation transforms the metal
atom X.sub.2.sup.0 present in the recording layer to crystalline
metal particles as shown in Reaction 1, and the resultant particles
that serve as "crystal nuclei" are uniformly dispersed in the
recording layer. In this way it is possible to readily initialize
recording material and to perform an initialization operation with
a uniform reflectivity distribution.
[0076] Since Au, Ag and Cu are effective additive elements that can
ensure storage reliability, it is possible to improve poor
initialization performance and to design phase-change materials
with excellent storage reliability.
[0077] Accordingly, the present invention focuses attention on the
rapid crystallization characteristics of X.sub.1--Sb compounds
(where X.sub.1 represents at least one element selected from Ga, Ge
and In) used for recording layer materials, and utilizes the
characteristics.
[0078] Meanwhile, poor initialization performance attributed to
higher crystallization temperatures is successfully improved by
adding at least one element selected from Au, Ag and Cu to the
recording layer material to form crystalline particles therein.
Thus, it is made possible to provide an optical recording medium
which can realize high-speed recording and high storage reliability
and whose recording material can be readily initialized to provide
a uniform reflectivity distribution.
[0079] In order to design phase-change materials suitable for
high-speed recording at as fast as 3.times. to 10.times.DVD
recording speeds, particularly at 8.times. or faster, the added
amount or level (.nu.) of any one of Au, Ag and Cu in the recording
layer material is set to 10 atomic % or less. Although these
elements provide excellent storage reliability and are effective
for improving poor initialization performance of high-speed
recording materials, they also reduce the crystallization rate of
the recording layer material to prevent high-speed recording. For
this reason, if the level of any one of Au, Ag and Cu in the
recording layer material is greater than 10 atomic %, it becomes
difficult to design phase-change materials suitable for high-speed
recording of 8.times. on DVD. Thus, the upper limit of the level of
any one of Au, Ag and Cu in the recording layer material needs to
be 10 atomic % or less; however, the lower limit is preferably 1
atomic % because when added in small amounts, effects brought about
by Au, Ag or Cu may be unclear.
[0080] With respect to the elemental ratios of Sb, Ga, Sb and Ge,
.alpha. in the foregoing Formula 1 needs to be 2 or greater. For
example, if X.sub.1 represents at least one of Ga and In and
.alpha. is less than 2, or if .beta. is less than 55, it results in
reduction in the crystallization rate and it becomes difficult to
perform an overwrite operation at a linear velocity of 28 m/s or
less, which is equivalent to 8.times.DVD recording speed. In
addition, if .alpha. is less than 2, it results in poor storage
reliability. At least one of Ga and In can increase the
crystallization rate even when added in small amounts. In
particular, Ga has an effect of increasing the crystallization
temperature of phase-change materials and serves as an element that
can effectively improve the stability of marks. However, if .alpha.
in Formula 1 is greater than 20, it becomes difficult to initialize
recording material. In particular, if Ga is added in small amounts,
the crystallization temperature becomes so high that it is
difficult to obtain a crystalline phase with a high, uniform
reflectivity distribution upon initialization. Meanwhile, In has a
similar effect as Ga and increases the crystallization temperature
to a level lower than that achieved by Ga. For this reason, in view
of problems associated with initialization, it is effective to use
In as a supportive element for Ga. In, however, reduces the
repetitive recording characteristics and causes a reduction in
reflectivity when added in excessive amounts; therefore, it should
be added at a level of 20 atomic % or less.
[0081] When X.sub.1 represents Ge only, it is possible to realize
recording material especially excellent in storage reliability
because Ge can, even when added in small amounts, significantly
increase the storage reliability without increasing the
crystallization temperature to a level equal to or higher than that
achieved by Ga. Ge has a specific effect of stabilizing
amorphization of a recording layer having high crystallization
rate, and such an effect is brought about when it is added at a
level of 2 atomic % or more; the greater the level, the greater the
effect. Ge, however, has a harmful effect that it reduces the
crystallization rate and, when added in excessive amounts, causes
an increase in jitter as a result of overwriting; therefore, it
should be added at a level of 20 atomic % or less. Even when the
level of Ge is 20 atomic %, the crystallization rate increases
rapidly, mark formation becomes difficult, and storage reliability
is reduced, if .beta. is greater than 95. Thus, .beta. should be 95
or less.
[0082] If X.sub.1 represents Ge and at least one of Ga and In, it
is also possible to obtain excellent storage reliability by
reducing the level of at least one of Ga and In, by increasing the
level of Ge to compensate this reduction, and by setting a to 2 or
greater.
[0083] In the second embodiment, the recording layer of the optical
recording medium of the present invention contains a composition
expressed by the following Formula 2
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
<Formula 2>
[0084] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; M represents at least one element selected from
elements other than X.sub.1, Sb and X.sub.2 and mixtures of the
elements other than X.sub.1, Sb and X.sub.2; and .alpha., .gamma.,
.gamma. and .delta. represent atomic % of their respective elements
(where 2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100)
[0085] In this case, the recording layer preferably contains a
composition expressed by the Following formula (2-1).
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
<Formula 2-1>
[0086] where X.sub.1 and X.sub.2 are identical to those in Formula
2; and .alpha., .beta., .gamma. and .delta. represent atomic % of
their respective elements (where 4.ltoreq..alpha..ltoreq.8,
65.ltoreq..beta..ltoreq.83, 4.ltoreq..gamma..ltoreq.8,
1.ltoreq..delta..ltoreq.20, and
(.alpha.+.beta.+.gamma.+.delta.)=100)
[0087] Here, the descriptions for X.sub.1 and X.sub.2 in the
foregoing Formulae 2 and 2-1 are similar to those provided in the
first embodiment.
[0088] The recording layer preferably contains a composition
expressed by the following Formula 3, where M is replaced with Sn
in Formula 2. By adding Sn in Ga--Sb materials as an essential
element as described above, it is possible to provide an optical
recording medium which can ensure excellent recording
characteristics and storage reliability even at high recording
speeds of 8.times. or faster on DVD.
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.--Sn.sub..delta.
<Formula 3>
[0089] where X.sub.1 and X.sub.2 are identical to those in Formula
2; and .alpha., .beta., .gamma. and .delta. represent atomic % of
their respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10,
0<6<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100)
[0090] The recording layer is expressed by the formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub.2).sub.-
.epsilon.Sn.sub..zeta.--Y.sub..eta. (where X.sub.2 represents at
least one element selected from Au, Ag and Cu; Y represents at
least one element selected from Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg,
Se, C, N, Mn and Dy; and .alpha., .beta., .gamma., .delta.,
.epsilon., .zeta. and .eta. preferably satisfy the following
conditions: 0.ltoreq..alpha..ltoreq.20, 0.ltoreq..beta..ltoreq.20,
0.ltoreq..gamma..ltoreq.20 (provided .alpha., .beta. and .gamma.
are not "0" at the same time), 40.ltoreq..delta..ltoreq.95,
0<.epsilon..ltoreq.10, 0.ltoreq..zeta..ltoreq.40,
0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.zeta.+.eta.)=100).
[0091] With respect to the elemental ratios of Sb, Ga, Ge and In,
if none of Ga, Ge and In is present, i.e.,
(.alpha.+.beta.+.gamma.)=0, it may result in poor storage
reliability. If .delta. is greater than 95, the crystallization
rate increases rapidly, mark formation becomes difficult, and
storage reliability is reduced, which are undesirable. If the level
of Ga is too high, the crystallization temperature becomes so high
that it is difficult to obtain a crystalline phase with a high,
uniform reflectivity distribution upon initialization. For this
reason, the level of Ga is preferably 20 atomic % or less.
Meanwhile, Ge provides an effect of improving storage reliability
when added at a level of about 2 atomic %; the greater the level,
the greater the effect. Ge, however, has a harmful effect that it
increases jitter as a result of overwriting when added in excessive
amounts; therefore, it should also be added at a level of 20 atomic
% or less. Meanwhile, In has a similar effect as Ga and increases
the crystallization temperature to a level lower than that achieved
by Ga. For this reason, in view of problems associated with
initialization, it is effective to use In as a supportive element
for Ga. In, however, reduces the repetitive recording
characteristics and causes a reduction in reflectivity when added
in excessive amounts; therefore, it should be added at a level of
20 atomic % or less. The level of Sn is preferably 40 atomic % or
less because it results in poor reproduction beam quality, poor
jitter performace, and poor storage reliability when added in
excessive amounts.
[0092] M preferably represents at least one element selected from
Te, Al, Zn, Mg, Tl, Pb, Sn, Bi, Cd, Hg, Se, C, N, Mn and Dy. Each
of these elements has its own effect of improving the recording
characteristics and storage reliability and thus can improve the
characteristics of X.sub.1--Sb--X.sub.2 alloys when added at
appropriate amounts.
[0093] In addition to Ga and In, Tl, Pb, Sn, Bi, Al, Zn, Mg, Cd and
Hg also have an effect of increasing crystallization limitation
velocity. Among these elements, Sn--an element with an atomic
number closest to that of Sb and potentially has a high
compatibility with Sb--is preferably used, increasing the
crystallization limitation velocity and improving overwriting
characteristics. The level of any of these elements is preferably
40 atomic % or less because it results in poor reproduction beam
quality and poor jitter performance when added in excessive
amounts.
[0094] In addition to Ge, Al, C, N and Se also have an effect of
improving storage reliability. Moreover, Al and Se contribute to
rapid crystallization, and Se contributes to an increase in the
recording sensitivity.
[0095] Furthermore, Mn and Dy have a similar effect as In. In
particular, Mn is an element excellent in storage reliability that
eliminates the need to increase the level of Ge too high. The
optimal level of Mn is 1 atomic % to 15 atomic %; if the level is
less than 1 atomic %, Mn never exhibits such an effect, whereas if
the level is greater than 15 atomic %, it results in too low
reflectivity in non-recorded portions (crystalline portions).
[0096] For the method for forming the recording layer, various
vapor deposition methods can be used--vacuum deposition, sputtering
method, plasma CVD, photo CVD, ion plating, electron-beam
deposition, or the like. Among these methods, the sputtering method
is excellent in terms of mass-productivity and film quality.
[0097] The thickness of the recording layer is not particularly
limited and can be appropriately determined depending on the
intended purpose; it is preferably 6 nm to 20 nm. If the thickness
of the recording layer is less than 6 nm, it results in a
significant reduction in the repetitive recording characteristics,
whereas if the thickness of the recording layer is greater than 20
nm, it results in an increase in the likelihood of recording layer
shifting as a result of overwriting, causing a significant increase
in jitter. Moreover, in order to increase information-erasing
characteristics by minimizing the difference in light-absorption
between the crystalline and amorphous phases, the recording layer
is preferably made thin. Thus, a preferable thickness range is 8 nm
to 16 nm.
[0098] Next, examples of the layer structure of the optical
recording medium of the present invention will be described with
reference to the drawings.
[0099] FIG. 1 is a schematic cross-sectional view of an example of
the optical recording medium of the present invention, where a
substrate 1 is provided, and a first protective layer 2, recording
layer 3, second protective layer 4, reflective layer 5 and resin
protection layer 6 are sequentially formed on the substrate 1.
[0100] FIG. 2 is a schematic cross-sectional view of another
example of the optical recording medium of the present invention,
where a substrate 1 is provided, and a first protective layer 2,
interface layer 7-1, recording layer 3, second protective layer 4,
reflective layer 5 and resin protection layer 6 are sequentially
formed on the substrate 1.
[0101] FIG. 3 is a schematic cross-sectional view of still another
example of the optical recording medium of the present invention,
where a substrate 1 is provided, and a first protective layer 2,
recording layer 3, interface layer 7-2, second protective layer 4,
reflective layer 5 and resin protection layer 6 are sequentially
formed on the substrate 1.
[0102] FIG. 4 is a schematic cross-sectional view of yet another
example of the optical recording medium of the present invention,
where a substrate 1 is provided, and a first protective layer 2,
recording layer 3, second protective layer 4, third protective
layer 8, reflective layer 5 and resin protection layer 6 are
sequentially formed on the substrate 1.
[0103] Note that another substrate may be bonded to the resin
protection layer 6 on an as-needed basis for further reinforcement
or protection of the optical recording medium.
--Substrate--
[0104] The substrate 1 needs to be made of material that can ensure
the mechanical strength of the optical recording medium. Moreover,
when a recording beam and reproduction beam are incident to the
optical recording medium after passing through the substrate 1, the
substrate 1 needs be transparent enough to admit beams of desired
wavelengths.
[0105] Examples of materials for the substrate include glass,
ceramics and resins; a substrate made of resin is preferably used
in view of the formability and costs of resin. Examples of the
resins include polycarbonate resins, acrylic resins, epoxy resins,
polystyrene resins, acrylonitrile-styrene copolymers, polyethylene
resins, polypropylene resins, silicone resins, fluorine resins, ABS
resins and urethane resins. Among these, polycarbonate resins and
acrylic resins are most preferable in view of their formability,
optical characteristics, and costs.
[0106] The thickness of the substrate 1 is not particularly
limited, and is generally determined depending on the wavelength of
laser beam used and on light-condensing characteristics of a pickup
lens. In CDs where a beam of 780 nm wavelength is used, a substrate
of 1.2 mm thickness is employed. In DVDs where a beam of 650 nm to
665 nm wavelength is used, a substrate of 0.6 mm thickness is
employed.
[0107] For the substrate, a substrate made of polycarbonate resin
is preferably used that is excellent in processibility and optical
characteristics. For example, such a substrate is a disc of 12 cm
in diameter and 0.6 mm in thickness, which has a tracking groove on
its surface. The tracking groove is preferably a wobble groove with
the following specification: pitch=0.74.+-.0.03 .mu.m; depth=22 nm
to 40 nm; and width=0.2 .mu.m to 0.4 .mu.m. The wobble groove
realizes accessing a particular non-recorded track, as well as
rotation of the substrate at a constant linear velocity. In
addition, increasing the depth of the grooves leads to a reduction
in reflectivity of the optical recording medium, making it possible
to increase the degree of modulation.
[0108] Note that an adhesion layer--a layer that serves to bond the
substrate 1 that records information signals to a dummy
substrate--is formed of any of a two-sided sheet, in which an
adhesive is applied on both sides of the base film, thermosetting
resin, and ultraviolet-curable resin. The thickness of the adhesion
layer is generally around 50 .mu.m.
[0109] The dummy substrate is not necessarily transparent in a case
where an adhesive sheet or thermosetting resin is used as an
adhesion layer. However, the dummy substrate is preferably
transparent in a case where ultraviolet-curable resin is used as
the adhesion layer. In general, the thickness of the dummy
substrate is preferably 0.6 mm like the transparent substrate 1 in
which information signals are to be written.
--First Protective Layer--
[0110] Preferably, the first protective layer 2 bonds well to the
substrate and recording layer and has high heat resistance.
Moreover, since the first protective layer 2 also serves as an
optical interference layer that enables the recording layer to
efficiently absorb light, it preferably has optical characteristics
suitable for repetitive recording at high linear velocities.
[0111] Examples of materials of the first protective layer include
metal oxides such as SiO, SiO.sub.2, ZnO, SnO.sub.2,
Al.sub.2O.sub.3, TiO.sub.2, In.sub.2O.sub.3, MgO and ZrO.sub.2;
nitrides such as Si.sub.3N.sub.4, AlN, TiN, BN and ZrN; sulfides
such as ZnS, In.sub.2S.sub.3 and TaS.sub.4; carbides such as SiC,
TaC, B.sub.4C, WC, TiC and ZrC; diamond carbon; and mixtures
thereof. Among these, mixtures of ZnS and SiO.sub.2 are preferable;
the molar ratio between ZnS and SiO.sub.2 (ZnS:SiO.sub.2) is
preferably 50 to 90:50 to 10, more preferably 60 to 90:40 to
10.
[0112] For the method for forming the first protective layer 2,
various vapor deposition methods can be used--vacuum deposition,
sputtering method, plasma CVD, photo CVD, ion plating,
electron-beam deposition, or the like. Among these methods, the
sputtering method is excellent in terms of mass-productivity and
film quality.
[0113] The thickness of the first protective layer 2 is not
particularly limited and can be appropriately determined depending
on the intended purpose; it is preferably 40 nm to 200 nm, more
preferably 40 nm to 100 nm. If the thickness of the first
protective layer 2 is less than 40 nm, the substrate may become
deformed because the substrate is also heated when the recording
layer is heated. If the thickness of the first protective layer 2
is greater than 200 nm, the mechanical strength of the disc may be
reduced to cause, for example, disc warpage.
--Second Protective Layer--
[0114] Preferably, the second protective layer 4 bonds well both to
the substrate and recording layer and has high heat resistance.
Moreover, since the first protective layer 2 also serves as an
optical interference layer that enables the recording layer to
efficiently absorb light, it preferably has optical characteristics
suitable for repetitive recording at high linear velocities.
[0115] Examples of materials for the second protective layer 4
include metal oxides such as SiO, SiO.sub.2, ZnO, SnO.sub.2,
Al.sub.2O.sub.3, TiO.sub.2, In.sub.2O.sub.3, MgO and ZrO.sub.2;
nitrides such as Si.sub.3N.sub.4, AlN, TiN, BN and ZrN; sulfides
such as ZnS, In.sub.2S.sub.3 and TaS.sub.4; carbides such as SiC,
TaC, B.sub.4C, WC, TiC and ZrC; diamond carbon; and mixtures
thereof. Among these, mixtures of ZnS and SiO.sub.2 are preferable;
the molar ratio between ZnS and SiO.sub.2 (ZnS:SiO.sub.2) is
preferably 50 to 90:50 to 10, more preferably 60 to 90:40 to
10.
[0116] For the method for forming the second protective layer 4,
various vapor deposition methods can be used--vacuum deposition,
sputtering method, plasma CVD, photo CVD, ion plating,
electron-beam deposition, or the like. Among these methods, the
sputtering method is excellent in terms of mass-productivity and
film quality.
[0117] The thickness of the second protective layer 4 is preferably
2 nm to 20 nm. Since the second protective layer significantly
affects the cooling down of the recording layer, the second
protective layer needs to be 2 nm or more in thickness in order to
ensure excellent information-erasing characteristics and repetitive
recording durability. If the thickness of the second protective
layer is less than 2 nm, it results in defects such as cracks and
repetitive recording durability is reduced. Moreover, it results in
poor recording sensitivity. If the thickness of the second
protective layer is greater than 20 nm, the cooling rate for the
recording layer is reduced and mark formation becomes difficult,
leading to small mark areas.
--Reflective Layer--
[0118] The reflective layer 5 functions not only as a light
reflection layer, but also as a heat-dissipating layer for
dissipating heat applied to the recording layer as a result of
laser beam irradiation during an recording operation. For the
cooling achieved by heat dissipation, the rate of which
significantly affects the formation of amorphous marks. For this
reason, selecting an appropriate reflective layer is important with
respect to phase-change optical recording media that can support
high linear velocity.
[0119] Examples of the materials for the reflective layer 5 include
metals such as Al, Au, Ag, Cu and Ta and alloys thereof. In
addition, Cr, Ti, Si, Cu; Ag, Pd, Ta and the like can be added to
these metals as an additive element. Among these, the reflective
layer 5 preferably contains either Ag or an Ag alloy. This is
because, in general, the reflective layer constituting the optical
recording medium is preferably made of metal with high thermal
conductivity and reflectivity from the view point of controlling
the rate of removal of heat generated upon recording as well as
from the optical view point of increasing the contrast of
reproduction signals by utilizing interference effects, and because
both Ag and an Ag alloy have a thermal conductivity of as high as
427 W/mK and thus can realize a rapid cooling mechanism suitable
for the formation of amorphous, by which the recording layer that
has reached a high temperature is immediately cooled down.
[0120] Although pure Ag is the best choice in light of its high
thermal conductivity, Cu may be added to it in order to impart
corrosion resistance. At this point, the level of Cu is preferably
0.1 atomic % to 10 atomic %, more preferably 0.5 atomic % to 3
atomic % so as not to adversely affects the characteristics of Ag.
When Cu is added in excessive amounts, the thermal conductivity of
Ag may be reduced.
[0121] The reflective layer 5 is formed with any of various vapor
deposition methods--vacuum deposition, sputtering method, plasma
CVD, photo CVD, ion plating, electron-beam deposition or the like.
Among these methods, the sputtering method is excellent in terms of
mass-productivity and film quality.
[0122] In general, the thickness of the reflective layer is
preferably 100 nm to 300 nm. If the thickness the reflective layer
is less than 100 nm, the reflective layer may not sufficiently
exert its function as a reflective layer. If the thickness of the
reflective layer is greater than 300 nm, it may result in poor
productivity or the mechanical strength of the disc may be reduced
to cause, for example, disc warpage.
--Third Protective Layer--
[0123] As shown in FIG. 4, the third protective layer 8 is
preferably provided between the second protective layer 4 and the
reflective layer 5.
[0124] Examples of the materials for the third protective layer 8
include Si, SiC, SiN, SiO.sub.2, TiC, TiO.sub.2, TiC--TiO.sub.2,
NbC, NbO.sub.2, NbV--NbO.sub.2, Ta.sub.2O.sub.5, Al.sub.2O.sub.3,
ITO, GeN and ZrO.sub.2. Among these, TiC--TiO.sub.2, Si or SiC is
preferably in light of their high barrier properties.
[0125] When a reflective layer containing pure Ag or an Ag alloy
and a protective layer containing sulfur (e.g., a mixture of ZnS
and SiO.sub.2) are used, diffusion of sulfur into Ag occurs to
cause disc defects (i.e., sulfuration of Ag). Thus, appropriate
materials that satisfy the following requirements need to be chosen
for the third protective layer 3 for preventing the occurrence of
such a reaction: (1) barrier properties to prevent the sulfuration
of Ag; (2) optical admittance of laser beams; (3) low thermal
conductivity for the formation of amorphous marks; (4) excellent
adhesiveness to the protective layer and/or reflective layer; and
(5) excellent formability, for example. Materials containing
TiC--TiO.sub.2, Si or SiC as a main constituent are preferable for
the third protective layer.
[0126] For the method for forming the third protective layer,
various vapor deposition methods can be used--vacuum deposition,
sputtering method, plasma CVD, photo CVD, ion plating,
electron-beam deposition, or the like. Among these methods, the
sputtering method is excellent in terms of mass-productivity and
film quality.
[0127] The thickness of the third protective layer is preferably 2
nm to 20 nm, more preferably 2 nm to 10 nm. If the thickness of the
third protective layer is less than 2 nm, the third protective
layer may not function as a barrier layer. If the thickness of the
third protective layer is greater than 20 nm, there is a likelihood
that modulation degree may be reduced.
--Interface Layer--
[0128] As shown in FIGS. 2 and 3, the interface layer 7-1 or
interface layer 7-2 is preferably provided at least between the
first protective layer 1 and recording layer 3 or between the
recording layer and second protective layer. Preferably, the
interface layer is made of at least one compound selected from
ZrO.sub.2, TiO.sub.2, SiO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5,
Y.sub.2O.sub.3, MgO, CaO, Nb.sub.2O.sub.5 and rare earth oxides.
Among these, SiO.sub.2 is most preferable.
[0129] The thickness of the interface layer is preferably 2 nm to
10 nm. By this, it is possible to reduce the damage of the
substrate caused as a result of high-power recording, thereby
achieving excellent repetitive recording characteristics upon
high-power recording. Thus, a wide recording power margin can be
ensured. If the thickness of the interface layer is less than 2 nm,
it may become difficult to form the interface layer uniformly,
whereas if the thickness of the interface layer is greater than 10
nm, the formed interface layer may be likely to fall off the
substrate.
[0130] It should be noted that the resin protective layer 6 can be
provided on the reflective layer 5 on an as-needed basis. The resin
protective layer 6 serves to protect the recording layer during the
manufacturing process or after the product is in service, and is
generally formed of ultraviolet-curable resin. The thickness of the
resin protective layer is preferably 2 .mu.m to 5 .mu.m.
[0131] The optical recording medium of the present invention can
also suitably be used as a multilayer optical recording medium. For
example, FIG. 5 is a schematic cross-sectional view of a
double-layer optical recording medium which sequentially includes
on a first substrate 10 a first information layer 18, intermediate
layer 20, second information layer 28 and second substrate 25, and
further includes an additional layer on an as-needed basis.
[0132] The first information layer 18 includes an adhesion layer
11, first lower protective layer 12, first recording layer 13,
first upper protective layer 14, first reflective layer 15, and
heat dissipation layer 16.
[0133] The second information layer 28 includes a second lower
protective layer 21, second recording layer 22, second upper
protective layer 23, and second reflective layer 24.
[0134] Note that a barrier layer may be provided between the first
upper protective layer 14 and first recording layer 15 and between
the second upper protective layer 23 and second reflective layer
24.
[0135] In the present invention it is preferable that at least one
of the first recording layer and second recording layer contains a
recording material of the present invention expressed by
X.sub.1--Sb--X.sub.2--Sn.
[0136] This multilayer optical recording medium realizes
high-capacity recording.
[0137] The optical recording medium of the present invention has
been described above. The present invention is not limited to the
embodiments described above, and various modifications can be made
without departing the scope of the present invention. For example,
the present invention can be applied in any form to a general
Blu-Ray optical recording medium as shown in FIG. 6, which has a
layered structure in which the first protective layer 32, recording
layer 33, second protective layer 34, reflective layer 36, and
dummy substrate 38 are sequentially provided on the substrate
31.
(Sputtering Target)
[0138] The sputtering target of the present invention is used for
the production of a recording layer, and in the first embodiment,
contains a composition expressed by the following Formula 1.
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.
[0139] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; and .alpha., .beta. and .gamma. represent
atomic % of their respective elements (where
2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, and (.alpha.+.beta.+.gamma.)=100)
[0140] In this case, the sputtering target preferably contains a
composition expressed by the Following formula (1-1).
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma. <Formula
1-1>
[0141] where X.sub.1 and X.sub.2 are identical to those in Formula
1; and .alpha., .beta., and .gamma. represent atomic % of their
respective elements (where 4.ltoreq..alpha..ltoreq.8,
84.ltoreq..beta..ltoreq.92, 4.ltoreq..gamma..ltoreq.8, and
(.alpha.+.beta.+.gamma.)=100)
[0142] Moreover, in the second embodiment the sputtering target of
the present invention used for the production of a recording layer
contains a composition expressed by the following Formula 2.
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
[0143] where X.sub.1 represents at least one element selected from
Ga, Ge and In; X.sub.2 represents at least one element selected
from Au, Ag and Cu; M represents at least one element selected from
elements other than X.sub.1, Sb and X.sub.2 and mixtures of the
elements other than X.sub.1, Sb and X.sub.2; and .alpha., .beta.,
.gamma. and .delta. represent atomic % of their respective elements
(where 2.ltoreq..alpha..ltoreq.20, 55.ltoreq..beta..ltoreq.95,
0<.gamma..ltoreq.10, 0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100)
[0144] In this case, the sputtering target preferably contains a
composition expressed by the Following formula (2-1).
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.-M.sub..delta.
<Formula 2-1>
[0145] where X.sub.1 and X.sub.2 are identical to those in Formula
2; and .alpha., .beta., .gamma. and .delta. represent atomic % of
their respective elements (where 4.ltoreq..alpha..ltoreq.8,
65.ltoreq..beta..ltoreq.83, 4.ltoreq..gamma..ltoreq.8,
1.ltoreq..delta..ltoreq.20, and
(.alpha.+.beta.+.gamma.+.delta.)=100)
[0146] In addition, M preferably represents at least one element
selected from Te, Al, Zn, Mg, Tl, Pb, Sn, Bi, Cd, Hg, Se, C, N, Mn
and Dy.
[0147] The sputtering target preferably contains a composition
expressed by the following Formula 3, where M is replaced with Sn
in Formula 2.
(X.sub.1).sub..alpha.Sb.sub..beta.(X.sub.2).sub..gamma.--Sn.sub..delta.
[Formula 3]
[0148] where X.sub.1 and X.sub.2 are identical to those in Formula
2; and .alpha., .beta., .gamma. and .delta. represent atomic % of
their respective elements (where 2.ltoreq..alpha..ltoreq.20,
55.ltoreq..beta..ltoreq.95, 0<.gamma..ltoreq.10,
0<.delta..ltoreq.40, and
(.alpha.+.beta.+.gamma.+.delta.)=100)
[0149] The sputtering target is expressed by the formula
Ga.sub..alpha.Ge.sub..beta.In.sub..gamma.--Sb.sub..delta.--(X.sub.2).sub.-
.epsilon.Sn.sub..zeta.--Y.sub..eta. (where X.sub.2 represents at
least one element selected from Au, Ag and Cu; Y represents at
least one element selected from Te, Al, Zn, Mg, Ti, Pb, Bi, Cd, Hg,
Se, C, N, Mn and Dy; and .alpha., .beta., .gamma., .delta.,
.epsilon., .zeta. and .eta. preferably satisfy the following
conditions: 0.ltoreq..alpha..ltoreq.20, 0.ltoreq..beta..ltoreq.20,
0.ltoreq..gamma..ltoreq.20 (provided .alpha., .beta. and y are not
"0" at the same time), 40.ltoreq..delta..ltoreq.95,
0<.epsilon..ltoreq.10, 0.ltoreq..zeta..ltoreq.40,
0.ltoreq..eta..ltoreq.10 and
(.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.zeta.+.eta.)=100).
[0150] The method for producing the sputtering target is not
particularly limited and can be appropriately determined depending
on the intended purpose; a predetermined amount of sputtering
target is measured into a glass ample, and is heated to melt.
Thereafter, the resultant sputtering target is pulverized with a
pulverizer, and the resultant power is heated and baked to provide
a disc-shaped sputtering target.
[0151] According to the present invention, it is possible to
provide an optical recording medium which is suitable for
high-speed recording at a speed of 8.times. on DVD, particularly at
8.times. or faster, even though its capacity is as high as that of
DVD-ROM, and which has a uniform reflectivity distribution after
initialized.
[0152] According to the present invention, it is also possible to
provide an optical recording medium with excellent repetitive
recording characteristics over a wide recording linear velocity
range, even though its capacity is as high as that of DVD-ROM, as
well as a sputtering target used for the manufacturing of the
optical recording medium.
(Method for Manufacturing Optical Recording Media)
[0153] The method of the present invention for manufacturing
optical recording media includes at least a recording
layer-formation step. In addition, this method includes an initial
crystallization step, and further includes an additional step on an
as-needed basis.
--Recording Layer-Formation Step--
[0154] The recording layer-formation step is a step for forming a
recording layer with a sputtering method using the sputtering
target of the present invention.
[0155] The sputtering method is not particular limited and can be
appropriately selected from those known in the art; for example,
sputtering is preferably performed under the following conditions:
Deposition gas=Ar gas; Input voltage=1 kW to 5 kW; and Deposition
gas flow rate=10 sccm to 40 sccm. The Ar gas pressure inside the
chamber during sputtering is preferably 7.0.times.10.sup.-3 mTorr
(mbar) or less.
--Initial Crystallization Step--
[0156] The initial crystallization step is a step for performing an
initial crystallization operation at a predetermined power density
to an optical recording medium rotating at a predetermined linear
velocity.
[0157] In general, vapor deposition methods are used for the
deposition of layers in a disc having a configuration as described
above, and vapor deposition is performed at low temperatures
because a resin-made substrate is used. Accordingly, since the
freshly prepared recording layer is one which has just been cooled
from a high-energy gaseous phase, it is amorphous and thus has low
reflectivity. Thus, it is preferable to form amorphous marks in the
crystalline recording layer to keep the reflectivity of the optical
recording medium higher. To achieve this, initialization is
required to crystallize information recording areas of the disc.
The initialization operation is performed by applying a
large-diameter, high-output laser beam on the periphery of the
recording layer, melting the recording layer, and gradually cooling
down the recording layer. Although any high-output laser beam and
optical system can be employed, a laser beam of about 800 nm
wavelength is generally employed. The output of the laser beam is
preferably 500 mW to 3,000 mW, more preferably 1,000 mW to 2,500
mW. The beam spot is preferably 0.5 .mu.m to 2.0 .mu.m in the
direction in which it is moved, and 30 .mu.m to 200 um in the
direction perpendicular to the direction in which it is moved. The
use of such a rectangular or oval beam spot can widen the
irradiation area. In view of the thermal and optical
characteristics of the optical recording medium, it is necessary to
set an optimal scanning speed and irradiation power.
[0158] In the optical recording medium the reflectivity
uniformity--expressed by the following Expression 1--is preferably
0.10 or less, more preferably 0.05 or less to recording and
reproduction laser beams of, for example, 600 nm wavelength applied
to the initialized non-recorded portions (crystalline portions). If
the reflectivity uniformity of after initialization is 0.10 or
less, it is possible to ensure uniform recording characteristics on
the entire surface of the disc Reflectivity uniformity=(maximum
reflectivity value-minimum reflectivity value)/average of
reflectivity values <Expression 1>
[0159] The optical recording medium preferably has a reflectivity
of 18% or more, more preferably 20% or more to recording and
reproduction laser beams of, for example, 600 nm wavelength applied
to the initialized non-recorded portions. If the reflectivity of
the optical recording medium to these laser beams is less than 18%,
reproduction and recording of signals may become difficult.
(The Method for Using Optical Recording Media)
[0160] The method of the present invention for using optical
recording media performs at least one of a recording operation,
reproduction operation, erasing operation, and rewriting
operation.
[0161] In this case, the recording linear velocity of an optical
recording medium is preferably equivalent to 8.times.DVD recording
speed--about 28 m/s.
[0162] More specifically, a recording laser beam (e.g., a
semiconductor laser beam) is applied through an objective lens onto
an optical recording medium from the substrate side, while rotating
the optical recording medium at a predetermined linear velocity.
The recording layer absorbs the applied laser beam and shows a
local temperature increase, forming marks with different optical
characteristics, for example. In this way information is recorded.
The information thus recorded can be reproduced by applying a laser
beam onto the optical recording medium rotating at a predetermined
linear velocity from the substrate side, and detecting the
reflected light beams.
(Optical Recording Apparatus)
[0163] The Optical recording apparatus of the present invention is
one which records information on an optical recording medium by
irradiating it with a laser beam emitted from a laser beam source,
wherein the optical recording medium of the present invention is
used as the optical recording medium.
[0164] The optical recording apparatus of the present invention is
not particularly limited and can be appropriately selected
depending on the intended purpose. For example, the optical
recording apparatus of the present invention includes a laser beam
source such as a semiconductor laser beam source for emitting a
laser beam; a collective lens for collecting the laser beam from
the laser beam source onto an optical recording medium attached to
the spindle; an optical device for guiding the laser beam from the
laser beam source both to the collective lens and a laser beam
detector; and the laser beam detector for detecting reflected
beams, and further includes an additional unit on an as-needed
basis.
[0165] The optical recording apparatus uses the optical device to
guide the laser beam emitted from the laser beam source to the
collective lens, and records information on the optical recording
medium by collecting the laser beam with the collective lens and
applying the collected laser beam onto the optical recording
medium. At this point, the optical recording apparatus guides
reflected beams to the laser beam detector, controlling the light
intensity of the laser beam source on the basis of the intensity of
laser beam detected by the laser beam detector.
[0166] The laser beam detector converts the laser beam intensity
into voltage or current and outputs it as an intensity signal.
[0167] Examples of the additional unit include a control unit; such
a control unit is not particularly limited as long as it can
control each unit, and can be appropriately selected depending on
the intended purpose. For example, equipment such as sequencers and
computers for applying an intensity-modulated laser beam can be
used.
[0168] According to the present invention, it is possible to
provide an optical recording medium which can maintain excellent
recording characteristics and storage reliability even at high
recording speeds of 3.times. to 10.times. on DVD, particularly at
8.times. or faster, and whose recording material can be readily
initialized to provide a uniform reflectivity distribution.
[0169] Hereinafter, the present invention will be described in
detail with reference to Examples, which however shall not be
construed as limiting the invention thereto.
EXAMPLE 1
--Preparation of Optical Recording Medium--
[0170] With a sputtering method (using Big Sprinter, a sputtering
device manufactured by Unaxis, Co. Ltd.), a first protective layer,
recording layer, second protective layer, third protective layer,
and reflective layer were sequentially deposited on a
substrate.
[0171] At first, a polycarbonate resin substrate of 12 cm in
diameter and 0.6 mm in thickness having a pattern of grooves with
constant track pitch of 0.74 .mu.m was prepared.
[0172] Next, with a sputtering method using a sputtering target of
(ZnS).sub.80(SiO.sub.2).sub.20 (mole %), the first protective layer
was deposited on the substrate to a thickness of 65 nm.
[0173] Next, with a sputtering method using a sputtering target of
Ga.sub.9Sb.sub.86Ag.sub.5 (atomic %), the recording layer was
deposited on the first protective layer to a thickness of 16 nm.
Here, sputtering was performed under the following conditions: Ar
gas pressure=3.0.times.10.sup.-3 Torr; and DC power=1.0 kW. Note
that the target of the recording layer was rendered disc shape by
measuring a predetermined amount of sputtering target into a glass
ample, heating it to melt, pulverizing the resultant sputtering
target with a pulverizer, and heating and baking the resultant
power. The elemental ratio of the deposited recording layer
analyzed by inductively coupled plasma (ICP) emission
spectrophotometric analysis was determined to be identical to that
of the sputtering target measured into the glass ample. A
sequential ICP emission spectrophotometric analyzer (SPS4000,
manufactured by Seiko Instruments, Inc.) was used for this
analysis. It should be noted also in Examples and Comparative
Examples to be described later that the alloy composition of the
recording layer is identical to that of the sputtering target.
[0174] Next, with a sputtering method using a sputtering target of
(ZnS).sub.80(SiO.sub.2).sub.20 (mole %), the second protective
layer was deposited on the recording layer to a thickness of 14
nm.
[0175] Next, with a sputtering method using a sputtering target of
SiC, the third protective layer was deposited on the second
protective layer to a thickness of 4 nm.
[0176] Next, with a sputtering method using a sputtering target of
pure Ag, the reflective layer was deposited on the third protective
layer to a thickness of 140 nm.
[0177] Next, acrylic curable resin was applied onto the reflective
layer by use of a spinner to a thickness of 5 .mu.m to 10 .mu.m,
and was irradiated with UV to form a resin protective layer.
[0178] Finally, a polycarbonate resin substrate of 12 cm in
diameter and 0.6 mm in thickness was bonded to the resin protective
layer by use of an adhesive. In this way the optical recording
medium of Example 1 was prepared.
EXAMPLE 2
--Preparation of Optical Recording Medium--
[0179] An optical recording medium of Example 2 was prepared in a
manner similar to that described in Example 1 except that the
composition of the recording layer was changed to
Ge.sub.16Sb.sub.79Ag.sub.5.
EXAMPLE 3
--Preparation of Optical Recording Medium--
[0180] An optical recording medium of Example 3 was prepared in a
manner similar to that described in Example 1 except that the
composition of the recording layer was changed to
In.sub.13Sb.sub.82Ag.sub.5.
EXAMPLE 4
--Preparation of Optical Recording Medium--
[0181] An optical recording medium of Example 4 was prepared in a
manner similar to that described in Example 1 except that the
composition of the recording layer was changed to
Ga.sub.9Ge.sub.3Sb.sub.85Ag.sub.3.
EXAMPLE 5
--Preparation of Optical Recording Medium--
[0182] An optical recording medium of Example 5 was prepared in a
manner similar to that described in Example 1 except that the
composition of the recording layer was changed to
Ga.sub.8In.sub.4Sb.sub.83Ag.sub.5.
EXAMPLE 6
--Preparation of Optical Recording Medium--
[0183] An optical recording medium of Example 6 was prepared in a
manner similar to that described in Example 1 except that the
composition of the recording layer was changed to
Ga.sub.9Sb.sub.81Ag.sub.5Te.sub.5.
EXAMPLE 7
--Preparation of Optical Recording Medium--
[0184] An optical recording medium of Example 7 was prepared in a
manner similar to that described in Example 1 except that the
composition of the recording layer was changed to
Ga.sub.11Sb.sub.84Ag.sub.2Mn.sub.3.
COMPARATIVE EXAMPLE 1
--Preparation of Optical Recording Medium--
[0185] An optical recording medium of Comparative Example 1 was
prepared in a manner similar to that described in Example 1 except
that the composition of the recording layer was changed to
Ga.sub.10Sb.sub.90.
<Initialization>
[0186] Initialization was performed in the following procedure:
Using PCR DISK INITIALIZER, an initializer manufactured by Hitachi
Computer Peripherals Co., Ltd., each optical recording medium was
rotated at a constant linear velocity and a laser beam with a power
density of 10 mW/.mu.m.sup.2 to 30 mW/.mu.m.sup.2 was applied onto
the optical recording medium while moving the laser beam at a
constant speed in the radial direction of the optical recording
medium.
<Evaluations>
[0187] The initialized optical recording media were evaluated for
their reflectivity distribution and recording characteristics in
the procedure described below. The results are shown in Tables 1 to
3.
--Reflectivity Distribution--
[0188] Evaluation of reflectivity distribution was made by
determining the reflectivity uniformity of reflectivity signals
obtained from the optical recording medium, i.e., (maximum
reflectivity value-minimum reflectivity value)/average of
reflectivity values). Meanwhile, evaluation of recording
characteristics was made in the following procedure: Using
DDU-1000, an optical disk evaluation device manufactured by Pulstec
Industrial Co., Ltd., which is equipped with an optical pickup
(NA=0.65, wavelength=660 nm), the C/N ratio was measured after 10
times 3T single pattern overwriting with EFM+modulation at a
recording linear velocity of 28 m/s (equivalent to 8.times.DVD
recording speed) and at a linear density of 0.267 .mu.m/bit. The
evaluation criteria are described below.
--Evaluation of Reflectivity Distribution--
[0189] Evaluation of reflectivity distribution was made based on
the criteria listed below with reference to the reflectivity of an
initialized DVD+RW disc supporting 2.4.times. recording, which is
commercially available (shown in Table 6 as a reference)
[0190] "A" . . . reflective uniformity is 0.05 or less is,
[0191] "B" . . . reflective uniformity is greater than 0.05 but
0.10 or less
[0192] "C" . . . reflective uniformity is greater than 0.10
[0193] In Comparative Example 1 the initialized recording layer was
observed with a transmission electron microscope (TEM), determining
the difference in the crystal conditions (see FIG. 7).
--Evaluation of Recording Characteristics--
[0194] It is reported that the C/N ratio needs to be at least 45 dB
or greater in order to achieve rewritable optical disc systems, and
that more stable systems can be achieved if the C/N ratio is 50 dB
or greater. In view of this fact, evaluation of recording
characteristics was made based on the criteria listed below.
[0195] "A" . . . C/N ratio is 50 dB or greater
[0196] "B" . . . C/N ratio is 45 dB or greater but less than 50
dB
[0197] "C" . . . C/N ratio is less than 45 dB TABLE-US-00001 TABLE
1 Example 1 Example 2 Example 3 Layer structure Reflective layer Ag
Ag Ag Third protective SiC SiC SiC layer Second protective
ZnS--SiO.sub.2 ZnS--SiO.sub.2 ZnS--SiO.sub.2 layer Recording layer
Ga.sub.9Sb.sub.86Ag.sub.5 Ge.sub.16Sb.sub.79Ag.sub.5
In.sub.13Sb.sub.82Ag.sub.5 First protective ZnS--SiO.sub.2
ZnS--SiO.sub.2 ZnS--SiO.sub.2 layer Substrate Polycarbonate
Polycarbonate Polycarbonate Evaluation results Signal pattern
Recording A A A characteristics Reflectivity A A B uniformity
[0198] TABLE-US-00002 TABLE 2 Example 4 Example 5 Example 6 Layer
structure Reflective layer Ag Ag Ag Third protective SiC SiC SiC
layer Second protective ZnS--SiO.sub.2 ZnS--SiO.sub.2
ZnS--SiO.sub.2 layer Recording layer
Ga.sub.9Ge.sub.3Sb.sub.85Ag.sub.3 Ga.sub.8In.sub.4Sb.sub.83Ag.sub.5
Ga.sub.9Sb.sub.81Ag.sub.5Te.sub.5 First protective ZnS--SiO.sub.2
ZnS--SiO.sub.2 ZnS--SiO.sub.2 layer Substrate Polycarbonate
Polycarbonate Polycarbonate Evaluation results Signal pattern
Recording B B B characteristics Reflectivity A A B uniformity
[0199] TABLE-US-00003 TABLE 3 Comparative Example 7 Example 1 Layer
Metallic reflective layer Ag Ag structure Third protective layer
SiC SiC Second protective layer ZnS--SiO.sub.2 ZnS--SiO.sub.2
Recording layer Ga.sub.11Sb.sub.84Ag.sub.2Mn.sub.3
Ga.sub.10Sb.sub.90 First protective layer ZnS--SiO.sub.2
ZnS--SiO.sub.2 Substrate Polycarbonate Polycarbonate Evaluation
Signal pattern results Recording characteristics B C Reflectivity
uniformity B C
[0200] The results shown in Tables 1 to 3 indicate that in Examples
1 to 7 the reflectivity distributions after initialization are all
small and, with respect to their recording characteristics, the C/N
ratios are all greater than 45 dB. By contrast, in Comparative
Example 1 where the recording layer contains no Ag, the
reflectivity distribution is remarkably broad compared to those in
Examples 1 to 7, leading to a conclusion that the reflectivity
uniformity is poor and the recording layer is not uniformly
initialized. In Comparative Example 1, excellent recording
characteristics were not obtained, due to large fluctuations of the
reflectivity signal.
[0201] FIG. 7 showing the state of the initialized recording layer
in Comparative Example 1 (observed with a transmission electron
microscope) reveals the non-uniform presence of small-diameter
crystal particles and large-diameter crystal particles (which are
not usually observed), which leads to a broad reflectivity
distribution.
EXAMPLE 8
--Preparation of Optical Recording Medium--
[0202] With a sputtering method (using Big Sprinter, a sputtering
device manufactured by Unaxis, Co. Ltd.), a first protective layer,
recording layer, second protective layer, third protective layer,
and reflective layer were sequentially deposited on a
substrate.
[0203] At first, a polycarbonate resin substrate of 12 cm in
diameter and 0.6 mm in thickness having a pattern of wobble grooves
with constant track pitch of 0.74 .mu.m was prepared.
[0204] Next, with a sputtering method using a sputtering target of
(ZnS).sub.80(SiO.sub.2).sub.20 (mole %), the first protective layer
was deposited on the substrate to a thickness of 65 nm.
[0205] Next, with a sputtering method using a sputtering target of
Ga.sub.11Sb.sub.72Ag.sub.2Sn.sub.15 (atomic %), the recording layer
was deposited on the first protective layer to a thickness of 16
nm. Here, sputtering was performed under the following conditions:
Ar gas pressure=3.0.times.10.sup.-3 Torr; and DC power=1.0 kW. Note
that the target of the recording layer was rendered disc shape by
measuring a predetermined amount of sputtering target into a glass
ample, heating it to melt, pulverizing the resultant sputtering
target with a pulverizer, and heating and baking the resultant
power. The elemental ratio of the deposited recording layer
analyzed by inductively coupled plasma (ICP) emission
spectrophotometric analysis was determined to be identical to that
of the sputtering target measured into the glass ample. A
sequential ICP emission spectrophotometric analyzer (SPS4000,
manufactured by Seiko Instruments, Inc.) was used for this
analysis. It should be noted also in Examples and Comparative
Example to be described later that the alloy composition of the
recording layer is identical to that of the sputtering target.
[0206] Next, with a sputtering method using a sputtering target of
(ZnS).sub.80(SiO.sub.2).sub.20 (mole %), the second protective
layer was deposited on the recording layer to a thickness of 10
nm.
[0207] Next, with a sputtering method using a sputtering target of
SiC, the third protective layer was deposited on the second
protective layer to a thickness of 4 nm.
[0208] Next, with a sputtering method using a sputtering target of
pure Ag, the reflective layer was deposited on the third protective
layer to a thickness of 140 nm.
[0209] Next, acrylic curable resin (produced by Dainippon Ink and
Chemicals, Incorporated) was applied onto the reflective layer by
use of a spinner to a thickness of 5 .mu.m to 10 .mu.m, and was
irradiated with UV to form a resin protective layer.
[0210] Finally, a polycarbonate resin substrate of 12 cm in
diameter and 0.6 mm in thickness was bonded to the resin protective
layer by use of an adhesive. In this way the optical recording
medium of Example 8 was prepared.
EXAMPLE 9
--Preparation of Optical Recording Medium--
[0211] An optical recording medium of Example 9 was prepared in a
manner similar to that described in Example 8 except that the
composition of the recording layer was changed to
Ga.sub.13Sb.sub.70Ag.sub.2Sn.sub.15.
EXAMPLE 10
--Preparation of Optical Recording Medium--
[0212] An optical recording medium of Example 10 was prepared in a
manner similar to that described in Example 8 except that the
composition of the recording layer was changed to
Ga.sub.4Ge.sub.7Sb.sub.69Ag.sub.35n.sub.17.
EXAMPLE 11
--Preparation of Optical Recording Medium--
[0213] An optical recording medium of Example 11 was prepared in a
manner similar to that described in Example 8 except that the
composition of the recording layer was changed to
Ga.sub.4Ge.sub.9Sb.sub.64Ag.sub.3Sn.sub.20.
EXAMPLE 12
--Preparation of Optical Recording Medium--
[0214] An optical recording medium of Example 12 was prepared in a
manner similar to that described in Example 8 except that the
composition of the recording layer was changed to
Ga.sub.10In.sub.2Sb.sub.70Ag.sub.3Sn.sub.15.
EXAMPLE 13
--Preparation of Optical Recording Medium--
[0215] An optical recording medium of Example 13 was prepared in a
manner similar to that described in Example 8 except that the
composition of the recording layer was changed to
Ge.sub.12Sb.sub.67Ag.sub.3Sn.sub.18.
EXAMPLE 14
--Preparation of Optical Recording Medium--
[0216] An optical recording medium of Example 14 was prepared in a
manner similar to that described in Example 8 except that the
composition of the recording layer was changed to
In.sub.18Sb.sub.70Ag.sub.3Sn.sub.4Te.sub.5.
EXAMPLE 15
--Preparation of Optical Recording Medium--
[0217] An optical recording medium of Example 15 was prepared in a
manner similar to that described in Example 8 except that the
composition of the recording layer was changed to
Ga.sub.4Ge.sub.8Sb.sub.68Ag.sub.2Sn.sub.15Mn.sub.3.
COMPARATIVE EXAMPLE 2
--Preparation of Optical Recording Medium--
[0218] An optical recording medium of Comparative Example 2 was
prepared in a manner similar to that described in Example 8 except
that the composition of the recording layer was changed to
Sb.sub.85Sn.sub.10Ag.sub.5.
[0219] The optical recording media (optical discs) prepared in
Examples 8 to 15 and Comparative Example 2 were initialized and
evaluated for their recording characteristics and storage
reliability.
<Initialization>
[0220] Initialization was performed in the following procedure:
Using PCR DISK INITIALIZER, an initializer manufactured by Hitachi
Computer Peripherals Co., Ltd., each optical disc was rotated at a
constant linear velocity and a laser beam with a power density of
10 mW/.mu.m.sup.2 to 30 mW/.mu.m.sup.2 was applied onto the optical
disc while moving the laser beam at a constant speed in the radial
direction of the optical disc.
<Evaluation of Recording Characteristics>
[0221] Evaluation of recording characteristics was made in the
following procedure: Using DDU-1000, an optical disk evaluation
device manufactured by Pulstec Industrial Co., Ltd., which is
equipped with an optical pickup (NA=0.65, wavelength=660 nm), the
C/N ratio was measured after 10 times 3T single pattern overwriting
with EFM+modulation at a recording linear velocity of 28 m/s
(equivalent to 8.times.DVD recording speed) and at a linear density
of 0.267 .mu.m/bit. The obtained C/N ratios were evaluated based on
the criteria listed below. The evaluation results are shown in
Tables 4-1 to 6.
[0222] Note that the C/N ratio needs to be at least 45 dB or
greater in order to achieve rewritable optical disc systems, and
that more stable systems can be achieved if the C/N ratio is 50 dB
or greater.
--Evaluation Criteria--
[0223] "C" . . . C/N ratio is less than 45 dB
[0224] "B" . . . C/N ratio is 45 dB or greater but less than 50
dB
[0225] "A" . . . C/N ratio is 50 dB or greater
<Crystallization Rate>
[0226] The crystallization limitation velocity described above
represents the characteristics of recording material, and means the
light beam linear velocity at which optical disc reflectivity shows
a rapid decrease as shown in FIG. 8, when a DC beam of constant
power is applied onto a rotating optical disc to evaluate the
dependency of optical disc reflectivity on light beam (note:
recording or reproduction beam) linear velocity, or rotational
speed of the optical disc. The evaluation method employing this
crystallization limitation velocity focuses on the limit of linear
velocity, beyond which crystallization (or information-erasing) is
impossible, when a recording or reproduction beam linear velocity
is continuously increased while regarding the "DC beam of constant
power" as a laser pulse (erasing pulse) of intermediate output
level described in the foregoing recording principle. In FIG. 8,
even when a DC beam is applied onto an optical disc at a high
linear velocity beyond the crystallization limitation velocity of
the recording material (donated by a heavy line in this drawing),
for example, it results in poor crystallization performance. The
evaluation results are shown in Tables 4-1 to 6
--Evaluation Criteria--
[0227] "B" . . . crystallization limitation veloctiy of optical
disc (see FIG. 8) is 20 m/s or greater
[0228] "C" . . . crystallization limitation velocity of optical
disc (see FIG. 8) is less than 20 m/s
<Recording Sensitivity>
[0229] The evaluation criteria of recording sensitivity are as
follows:
[0230] "B" . . . optimal laser power required to record patterns is
less than 40 mW
[0231] "C" . . . optimal laser power required to record patterns is
40 mW or greater
[0232] The evaluation results are shown in Tables 4-1 to 6.
<Reflectivity After Initialization>
[0233] The reflectivity of the initialized non-recorded portions to
recording and reproduction laser beams (wavelength=660 nm) was
measured with the foregoing optical disk evaluation device under
the following condition: reproduction rate=3.5 m/s; read power=0.7
mW. The evaluation results are shown in Tables 4-1 to 6. It should
be noted that the reflectivity of the initialized non-recorded
portions to recording and reproduction laser beams (wavelength=660
nm) is preferably 18% or more, more preferably 20% or more. If the
reflectivity is less than 18%, reproduction and recording of
signals may become difficult.
--Evaluation Criteria--
[0234] "B" . . . reflectivity is 18% or more
[0235] "C" . . . reflectivity is less than 18%
<Reflectivity Uniformity>
[0236] The reflectivity of the initialized non-recorded portions to
recording and reproduction laser beams (wavelength=660 nm, NA=0.65)
was measured with the foregoing optical disk evaluation device
under the following condition: reproduction rate=3.5 m/s; read
power=0.7 mW. The evaluation results are shown in Tables 4-1 to
6.
--Evaluation Criteria--
[0237] Evaluation of reflectivity distribution was made based on
the criteria described below with reference to the reflectivity of
an initialized DVD+RW disc supporting 2.4.times. recording, which
is commercially available (shown in Table 6 as a reference).
[0238] "A" . . . reflective uniformity is 0.05 or less is,
[0239] "B" . . . reflective uniformity is greater than 0.05 but
0.10 or less
[0240] "C" . . . reflective uniformity is greater than 0.10
<Evaluation of Storage Reliability>
[0241] The optical discs prepared in Examples 8 to 15 and
Comparative Example 2 were placed into a constant-temperature bath
(80.degree. C., 85% RH) for 300 hours. After this, their C/N ratios
were determined to evaluate the storage reliability based on the
criteria listed below. The evaluation results are shown in Tables
4-1 to 6.
<Evaluation Criteria>
[0242] "A" . . . C/N ratio after placed in a constant-temperature
bath (80.degree. C., 85% RH) for 300 hours is 50 dB or greater
[0243] "B" . . . C/N ratio after placed in a constant-temperature
bath (80.degree. C., 85% RH) for 300 hours is 45 dB or greater but
less than 50 dB
[0244] "C" . . . C/N ratio after placed in a constant-temperature
bath (80.degree. C., 85% RH) for 300 hours is less than 45 dB
[0245] Note that a symbol "-" is provided for non-evaluated items.
TABLE-US-00004 TABLE 4-1 Example Example 8 Example 9 Recording
material Ga.sub.11Sb.sub.72Ag.sub.2Sn.sub.15
Ga.sub.13Sb.sub.70Ag.sub.2Sn.sub.15 Evaluation Recording A A
results characteristics Crystallization rate B B Recording
sensitivity B B Reflectivity after B B initialization Reflectivity
uniformity A B Storage reliability B B Signal pattern
[0246] TABLE-US-00005 TABLE 4-2 Example Example 10 Example 11
Recording material Ga.sub.4Ge.sub.7Sb.sub.69Ag.sub.3Sn.sub.17
Ga.sub.4Ge.sub.9Sb.sub.64Ag.sub.3Sn.sub.20 Evaluation results
Recording A A characteristics Crystallization rate B B Recording
sensitivity B B Reflectivity after B B initialization Reflectivity
uniformity A A Storage reliability A A Signal pattern
[0247] TABLE-US-00006 TABLE 5-1 Example Example 12 Example 13
Recording material Ga.sub.10In.sub.2Sb.sub.70Ag.sub.3Sn.sub.15
Ge.sub.12Sb.sub.67Ag.sub.3Sn.sub.18 Evaluation results Recording B
B characteristics Crystallization rate B B Recording sensitivity B
B Reflectivity after B B initialization Reflectivity uniformity A A
Storage reliability B A Signal pattern
[0248] TABLE-US-00007 TABLE 5-2 Example Example 14 Example 15
Recording material In.sub.18Sb.sub.70Ag.sub.3Sn.sub.4Te.sub.5
Ga.sub.4Ge.sub.8Sb.sub.68Ag.sub.2Sn.sub.15Mn.sub.3 Evaluation
results Recording B A characteristics Crystallization rate B B
Recording sensitivity B B Reflectivity after B B initialization
Reflectivity uniformity B B Storage reliability B B Signal
pattern
[0249] TABLE-US-00008 TABLE 6 Comparative Example Example 2
Reference Example Recording material Sb.sub.85Sn.sub.10Ag.sub.5 DVD
+ RW supporting 2.4x Evaluation results Recording C --
characteristics Crystallization rate B -- Recording sensitivity C
-- Reflectivity after B B initialization Reflectivity uniformity C
A Storage reliability C Signal pattern
[0250] The results shown in Tables 4-1, 4-2 and 5-2 indicate that
both recording characteristics and storage reliability were
excellent in Examples 8 to 15--the C/N ratios were all 45 dB or
greater even after a 300-hour endurance test in a
constant-temperature bath (80.degree. C., 85% RH). In particular,
C/N ratios of as high as 50 dB or greater were achieved in Examples
8 to 11 and 13, where Ga--Sb recording material or Ga--Ge--Sb
recording material was used.
[0251] Moreover, Examples 10, 11 and 13, where a recording layer
containing Ge was used, offered no reduction in the recording
characteristics even after a 300-hour endurance test in a
constant-temperature bath (80.degree. C., 85% RH). Examples 11 and
12, where a recording layer containing In was used, offered small
C/N ratios compared to that in Example 8 because In does not
increase the crystallization rate too much, as does Ga. In spite of
this, Examples 11 and 12 offered CN ratios as high as 45 dB or
greater, with the expectation that excellent recording
characteristics would be provided. In addition, Example 14 offered
excellent storage reliability by virtue of the presence of Te,
though the recording layer in this Example does not contain Ge and
has a high Sb ratio.
[0252] Since the recording layer in Comparative Example 2 does not
contain at least one element selected from Ga, Ge and In, it
resulted in poor recording characteristics and storage reliability,
though the crystallization rate and reflectivity uniformity after
initialization were excellent.
[0253] The optical recording medium of the present invention can be
suitably used for various optical recording media such as CD-R,
CD-RW and DVD--particularly for high-speed optical recording media
supporting 3.times. to 10.times.DVD recording speeds, particularly
8.times. or faster. Moreover, the optical recording medium of the
present invention can also be applied to various rewritable
(phase-change) optical recording media ranging from optical
recording media using a CAV recording technology to record at a
maximum speed of 8.times.DVD+RW recording to low-compatible optical
recording media supporting 3.times. speed recording.
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